1. Field of Invention
This invention relates to paper-plastic and paper-plastic-paper laminates in the form of sheeting which is capable of being converted into a self-closing package or other material such as envelopes, bags and other dilatable container products which initially are in a flat state and are normally made of paper. In these laminates, a paper facing sheet is cold-laminated to an oriented film of synthetic plastic material, or two paper sheets are cold laminated to the film.
2. Status of Prior Art
The sheeting traditionally used in making envelopes, grocery bags and other types of dilatable container products which initially are in a flat state is paper. Paper is a semi-synthetic material made by chemically processing cellulose fibers.
Apart from its low cost, an important advantage of paper is that it can be converted into envelopes and other types of dilatable container products by means of high speed equipment that functions to cut and fold the sheeting into the desired configuration, the folds and flaps of the product being bonded together, where necessary, by standard low-cost adhesives. Another advantage of paper in this context is that it can readily be printed and colored, using standard inks for this purpose.
But such paper products suffer from several disadvantages, for they are characterized by low tear and burst strength, and are by no means water resistant; for unless coated, paper is highly absorbent.
Also well known in the art are plastic-coated cellulosic papers, these being used chiefly in children""s books, posters, signs and shipping tags, and for other purposes demanding resistance to hard wear and to outdoor exposure. However, such plastic-coated papers lack high tear and burst strength. Also low in strength are special purpose coated papers covered on one or both sides with a suspension of clays, starches, rosin or wax, or a combination of these substances.
To overcome the drawbacks of paper-fabricated dilatable container products, in recent years such products have been made of TYVEC or other polymeric synthetic plastic sheeting. The resultant products not only have a tear and bursting strength far superior to paper, but they are also waterproof.
However, TYVEC and similar synthetic plastic sheeting is difficult to convert into envelopes and other dilatable container products using high-speed equipment of the type mainly suitable for paper. As a consequence, production scrap rates can run as high as thirty percent, thereby raising the cost of manufacturing these products. Moreover, such plastic sheeting has a low chemical affinity for standard adhesives; hence in the case of envelopes, one must then use a special and more costly adhesive on the flaps. And such plastic sheeting also has a low affinity for standard printing inks, and the products, therefore, demand special printing inks for this purpose.
The invention relates to a flexible paper-plastic laminate sheeting capable of being converted by conventional equipment into envelopes, bags and other dilatable container products normally made of paper which initially are in a flat state. The laminate sheeting comprises:
(a) a first paper facing sheet having first and second surfaces; and
(b) a reinforcing film of a synthetic oriented polymer comprising polyethylene or polypropylene, the film having a first and second surfaces, one of which is treated to increase its dynes and its affinity to adhesives, the treated surface of the film being cold-laminated by a water-based adhesive to the first surface of the paper facing sheet whereby products made from the sheeting have a printable paper exterior and exceptional tear and burst strength.
In a preferred embodiment, a second paper facing sheet having first and second surfaces is cold-laminated by a water-based adhesive to the first surface of the second paper facing sheet to produce a non-curling, three-ply laminate sheeting having exterior surfaces of the first and second printable paper sheets. To facilitate this, the second surface of the reinforcing film is treated to increase its dynes and its affinity to adhesives. In the three ply embodiment, the reinforcing film can instead be polyester.
The invention also relates to a method of making a flexible paper-plastic laminate sheeting capable of being converted by conventional equipment into envelopes, bags and other dilatable container products normally made of paper which initially are in a flat state. This method comprises providing a supply of a first paper sheet having first and second surfaces; providing a supply of a reinforcing film of a synthetic plastic material having first and second surfaces; orienting the film of plastic material to increase its strength; treating the first surface of the film to increase its dynes and its affinity to adhesives; applying a water-based adhesive to the treated first surface of the film; and cold-laminating the adhesive bearing first film surface to the first surface of the paper sheet to form a laminate sheeting that has a paper surface and exceptional tear and burst strength.
Another embodiment of this method further comprises providing a supply of a second paper sheet having first and second surfaces; treating the second surface of the film to increase its dynes and its affinity to adhesives; applying a water-based adhesive to the treated second surface of the film; and cold-laminating the adhesive bearing second film surface to the first surface of the second paper sheet to form a non-curling, three-ply laminate sheeting that has outer printable paper surfaces and exceptional tear and burst strength.